1. Field of the Invention
The present invention pertains to a circulation reversing tool for reversing the flow of drilling fluid in a well borehole at the nozzles of an oil well tool such as a drill bit. More particularly, the invention relates to a novel circulation reversing tool which upon a predetermined command will provide either a conventional circulation system in which drilling fluid travels down inside the drill string through the nozzles of the drill bit and back up the annulus, or which will reverse the circulation of the drilling fluid at a predetermined point along the drill string to result in drilling fluid flowing down the borehole annulus and into the nozzles of the drill bit and up the inside of the drill string to the predetermined point in the drill string without removing the drill string or circulation reversing tool from the well borehole. The circulation above the predetermined point on the drill string remains conventional notwithstanding changes in circulation below the predetermined point which changes in circulation do not interfere with drilling operations.
The circulation reversing tool includes a body divided into upper and lower portions in which the lower portion includes internal passages connecting the borehole annulus with the interior of the tool above and below a seal that is rotatably mounted on the body of the tool. The body of the tool includes a telescoping member threaded into the drill string having a rotatable diverter to alternatively engage the internal passages in the body to provide a conventional circulation pattern at a point above the seal and alternatively provide either a conventional or reverse circulation pattern below the seal upon command from the surface. The circulation reversing tool provides numerous advantages over prior art reverse circulation tools and allows drilling to be converted from conventional circulation to reverse circulation without removing the drill string from the borehole to increase the rate of removal of cuttings from the well faster and increase drill bit life while eliminating the problems of down time in trips to change the tool. The novel circulation reversing tool provides advantages in cleaning the borehole walls and in isolating producing zones in existing wells while drilling and providing numerous advantages heretofore unavailable in the prior art.
1. Description of the Prior Art
The prior art includes a variety of oil well tools for modifying the flow characteristics of the drilling fluid above the drill bit. A number of these prior art devices pertain to modifying the angular flow or velocity of drilling fluid above or around the drill bit while some tools are designed specifically to provide a complete reverse circulation system. A few prior art systems as described in patents such as Marais U.S. Pat. No. 4,223,747 and Franks, Jr. U.S. Pat. Nos. 4,285,408 and 4,312,415 pertain to reverse circulation tools designed to change the circulation of the drilling fluid above the drill bit in the borehole annulus. The prior art reverse circulation tool systems pertain to devices which when placed on the drill string convert a conventional or traditional flow system, in which drilling fluid goes down the interior of the drill string and out through the nozzles of the drill bit and up the borehole annulus, to a reverse circulation system at a point below the addition of the reverse circulation tool.
These prior art reverse circulation tools change the circulation path below the tool by diverting drilling fluid or mud from the interior of the drill string to the borehole annulus below the tool so that drilling fluid travels down the borehole annulus and in the nozzles of the drill bit and up the interior of the drill string to the reverse circulation tool and then exits through the sides of the drilling tool and up the borehole annulus above the reverse circulation tool. The best available known prior art reverse circulation tools require the removal of the entire drill string from the borehole annulus along with the circulation reversing tool and the subsequent disassembly of the tool in order to convert the system from a conventional to a reverse circulation system or back again. The requirement for the removal of the drill string and tool from the borehole annulus limits the advantages in converting from conventional to reverse circulation particularly in instances where the drill bit is stuck.
These limitations in the known prior art reverse circulation tools results in a change in circulation only during a trip or the removal of the drill string from the borehole annulus. The reverse circulation tools such as Franks, Jr. U.S. Pat. Nos. 4,285,408 and 4,312,415 allow a change from conventional to reverse circulation below the point of installation of the tool while maintaining traditional circulation above the tool. Such prior art reverse circulation tools like the ones previously discussed require the removal of the drill string from the borehole and disassembly of the tool to mechanically realign the ports to change conventional circulation to a reverse circulation system. This interruption in drilling required to remove and rack the drill string and then subsequently reconnect and replace the drill string back in the borehole limits the advantages of reverse circulation and is particularly apparent in cases where the drill bit becomes stuck.
Reversing circulation of drilling fluid at the drill bit while maintaining conventional circulation at a point above the drill bit provides numerous advantages during drilling including imparting a longer drill bit life by providing a more efficient circulation pattern and reducing the weight of the drilling collars to relieve pressure on the drill bit. Other advantages include a reduction in the fluid pump pressure, providing greater volume of drilling fluid to allow more footage to be made with less trip time in removing the drill pipe from the well borehole and reducing the number of changes of the bit.
These and other known advantages to reverse circulation however are in many cases offset by the limitations in prior art reverse circulation tools which require the removal of the entire drill string and tool from the borehole annulus to change from a conventional to a reverse circulation drilling system. The disadvantages and limitations of the prior art reverse circulation systems and in some cases the special equipment or tools required to remove or change the reverse circulation tool has limited the acceptance of such tools in modern high speed drilling operations which attempt to reduce the number of trips and down time required to remove the drill string from the borehole annulus. The cost and expense of rig time is often offset against the loss and cost of drill bits as a result of the time required to remove the drill string and rack drill pipe, which is usually 30 feet in length, to change over from conventional circulation to reverse circulation.
The present invention, unlike the prior art, provides a circulation reversing tool which upon a command from the surface changes from conventional circulation to reverse circulation and back again from reverse circulation to conventional circulation. The novel tool of the invention allows repeated changes in circulation without removing the drill string or drill bit from the borehole annulus thereby eliminating the time and expense required to remove, rack and mechanically change the most advanced prior art reverse circulation tools to change from a conventional circulation pattern to a reverse circulation pattern. The circulation reversing tool of the invention is furthermore compatible with both a conventional and reverse circulation system to provide the advantages of modifying the circulation flow pattern at the drill bit without removing the drill string. These and other features of the invention are particularly advantageous in freeing a drill bit that may become stuck during drilling operations. Unlike the prior art, the novel circulation reversing tool of the invention allows a change in circulation upon command from the surface without removing the drill string and without significant interruption of the drilling operation.